I encourage you to read the article, and subscribe to Sean’s blog, as it provides some valuable insite. I think this statement sums things up quite nicely:

The three options for data access are still the same “Web Services, WCF Data Services and WCF RIA Services”. My major issue with data access today in Silverlight persists: there is no perfect answer. There is give and take with each approach and giving good advice about the right one is difficult.

Sean also provided a very nice chart that quickly outlines these options: